Activation of peripheral ATP-sensitive K+ channels mediates the antinociceptive effect of Crotalus durissus terrificus snake venom

The role of peripheral potassium channels on the antinociceptive effect of Crotalus durissus terrificus venom, a mixed delta- and kappa-opioid receptor agonist, was investigated in hyperalgesia induced by carrageenin or prostaglandin E-2. Rat paw pressure test was applied before and 3 h after the intraplantar (i.pl.) injection of the nociceptive stimuli. Oral administration of venom 2 h after carrageenin or prostaglandin E-2 induces antinociception. Local pretreatment with 4-aminopyridine and tetraethylammonium (blockers of voltage-dependent K+ channel) or charybdotoxin and apamin (inhibitors of large- and small-conductance Ca2+-activated K+ channel, respectively) did not modify venom effect. On the other hand, glybenclamide, an inhibitor of ATP-sensitive K+ channel abolished antinociception induced by the venom. Glybenclamide also inhibited the antinociceptive effect Of [D-Pen(2.5)] enkephalin (DPDPE), a delta opioid receptor agonist, but did not modify the effect of (+)-trans-(1R,2R)-U-50488 (U50488), a kappa opioid receptor agonist. Diazoxide and pinacidil, two ATP-sensitive K+ channel openers, injected by intraplantar route, induced a long-lasting increment of pain threshold of the animals and produced antinociception in both models of hyperalgesia. These results suggest that the antinociceptive effect of crotalid venom is mediated by activation of ATP-sensitive K+ channels at peripheral afferent neurons. (C) 2003 Elsevier Science B.V. All rights reserved.